Novel corrosion inhibiting thermoplastic alloys can be prepared by blending corrosion inhibitors with selected engineering plastics having high hardness and which are suitable for injection molding. In accordance with the present invention, higher melting durable blends of a resinous engineering plastic and a selected corrosion inhibitor are produced in order to form improved molded objects or moldings useful for long term protection of metallic objects and/or electronic media devices against corrosion, including, for example, multi-faced enclosures fabricated from top, bottom and side panels, with the panels being fabricated in accordance with the present invention. Such multi-faced enclosures are known in the art. Higher melting polymers characterized as engineering plastics such as nylon, polyesters (PET) or polycarbonates such as Lexan can be blended with selected corrosion inhibitors to create working formulations which are adaptable for direct application in high temperature operations such as injection molding. For example, the selected corrosion inhibitors are retained in-situ with minimal loss during the molding operation or cycle and yet will subsequently slowly vaporize and/or sublime around the devices being retained within the enclosure to provide corrosion protection for long term use and/or storage.
Flexible films incorporating vapor corrosion inhibitor chemicals have been available and are used widely for the protection of metallic articles in storage and shipping. Such applications are especially useful for sensitive electronic media devices and other delicate metallic articles. Paper has also been coated with vapor corrosion inhibitors and is used extensively for protection of metallic articles during storage and shipping. Vapor phase corrosion chemicals are also available in small pellets and packages, and may also be impregnated into plastic foam to provide other methods of protection. All of the above methods are typically temporary in nature, in contrast to the products of the present invention which can provide years of protection particularly in enclosed or confined areas.
The most effective inhibitors volatilize easily and this volatility feature has been found in the past to preclude their use in the higher melting thermoplastic systems. Selected improved corrosion inhibiting formulations, in combination with high temperature engineering plastics including nylon, polyesters and/or polycarbonates provide a unique feature when treated in accordance with the present invention, inasmuch as the corrosion inhibitors become semi-permanently encapsulated or partially solubilized within the resin matrix, and thereafter leach out at a slow rate which provides ongoing protection over an extended period of time.
In accordance with the present invention, it has been determined that the selected higher melting engineering plastic resins can be blended with selected higher melting corrosion inhibiting chemicals in a masterbatch formulation containing about 85 parts resin and 15 parts inhibitors. This masterbatch can be blended further with the resin to produce a working formulation or mix containing about 1-7.5% inhibitors, balance resin, and with this formulation being suitable for injection molding.
Typical articles prepared with from 1 to 7.5% inhibitor in a the resin mix are knife holders, components for electronic devices and/or articles, enclosures for delicate electronic systems, and other injection molded pieces utilized in enclosing and protecting metallic articles against corrosion from corrosive elements in t atmosphere and/or ambient. These enclosures for delicate electronic systems, for example, typically comprise multi-faced enclosures fabricated from top, bottom and side panels which are, in turn, prepared pursuant to the features of the present invention.
Therefore, it is a primary object of the present invention to provide an improved molding compound capable of receiving and retaining a vapor phase corrosion inhibitor, with the compound thereafter being subjected to an injection molding operation to form an article to ultimately release a corrosion inhibitor in vapor phase from within the body or structure of a molded article and forming a protective environment. Because of the requirements of high temperature engineering plastics of the present invention, nylon, polesters and polycarbonates have been found to be most uniquely and advantageously utilized inasmuch as they are compatible with and may be readily filled with a quantity of selected granular, pulverulent or powder form corrosion inhibitor. The melting point of the base resin is such that the selected corrosion inhibitors remain soluble, are not released, and do not become fugitive during exposure to conditions required in the injection molding operation. Such a combination of properties is important inasmuch as exposure to relatively high temperatures for finite periods of time such as during a molding operation, is normally adequate to cause certain corrosion inhibiting compounds, when combined with other resins, to flash, sublime or otherwise become lost during the molding process. By use of carefully selected corrosion inhibitors and high temperature engineering plastics together with appropriate blending and masterbatch techniques, a suitable molding material may be made from these resins with the selected corrosion inhibiting compounds being retained in the plastic matrix throughout the process.
It is a further object of the present invention to employ a technique such as a masterbatch preparation which has been found to preserve the quality and character of the corrosion inhibitor in the resin matrix for a period of time suitable for achieving an appropriate shelf life, during which the pre-blended masterbatch is extended with additional quantities of resins in preparation of the working formulation or blend suitable for the injection process.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification and appended claims.
Masterbatches embodying features of the present invention are prepared using engineering plastics or resins found suited for injection molding applications, all in accordance with the present invention. These masterbatches are preferably blended with selected corrosion inhibitors at a ratio of 85 parts resin and 15 parts inhibitor or in some cases and with certain equipment, may be used as is, without blending. The select inhibitors suitable for this process are higher melting types including sodium nitrite, cyclohexylammonium-benzoate, benzotriazole, and sodium sebacate. Formulations of selected inhibitors that have been found suited for blending with these higher melting engineering resins and which are particularly effective contain the following components:
Another formulation found to be especially compatible with these resins is as follows:
In the event the metallic articles to be protected do not include copper, Formula 2 set forth above is an effective inhibitor combination.
Those Nylon 6 resins produced by Monsanto, such as those sold under the trade designations xe2x80x9cVydyne M-344-01xe2x80x9d have been found to function effectively when used as the carrier resin in the masterbatch and also function well as the further extender for the masterbatch when mixed to produce the working blend needed for injection molding operation. In addition to Nylon 6, other polyamide polymers properly characterized as nylons may also be employed, such as, for example, Nylons 9, 11, and 12. Furthermore, those certain nylons obtained as the result of a condensation product of an acid such as adipic acid, and a diamine such as hexylmethylenediamine may be employed. These condensation products include, by example, Nylon 66 as well as others such as Nylon 88 and Nylon 610. Each of these nylons is properly characterized as an engineering plastic.
Typical specific examples describing the invention are as follows: